This invention relates to printing presses, particularly to web presses, and has special applicability to a special form of web press which is known as a forms press, used to manufacture printed business forms which combine unique printed material with various physical attributes. These include cross-perforations which delineate successive forms that are connected and zig-zag folded, line feeding perforations which are usually marginal, other perforations to define separable segments of the forms, and successive numbering of the individual forms. A typical forms press of this type is described in U.S. Pat. No. 4,177,730; current models of such a press include provisions for changing the size of the printing and processing cylinders of such a press.
Business forms are rapidly increasing in use, particularly single-part forms, and the demand is extending into so-called short run forms, where a customer may only order a relatively small quantity, for example 5,000 to 10,000 forms. The makeready of the press, particularly of the offset printing units or towers, occupies a greater percentage of the total run time in shorter runs. In order to control costs, keep prices reasonable, and still meet the demand for these relatively smaller orders of business forms, the forms manufacturing industry needs a forms press which requires a minimum of makeready, can operate at different speeds (which may vary considerably) up to a reasonably fast printing speed (e.g. 500 ft./min), preferably can make changes in the printed material of the form without time consuming shut-down and makeready, and which has the capability of providing a wide variety of forms.
Various attempts have been made to adapt laser printing systems to the printing of variable information on pre-printed webs. Those systems utilize powder developers, which are quite expensive when their particle size is reduced to increase resolution to that comparable to other types of printing such as lithography. Furthermore, such particle size reduction makes powder toners even more difficult to handle, and increases the already present serious problems of pollution control as part of handling such powder developers. Equipment maintenance is also a potential problem with powder toner systems, because the attendant "powder cloud" permeates the equipment and its ambience, and tends to deposit on surfaces such as corona wires, lenses, belts, etc. where such deposit adversely affect operation, beyond being a clean-up nuisance.
Relatively sophisticated copy machines have been developed, using powder toner, and while a few of these have capability of printing on web material those units are essentially a variation of similar sheet fed copiers. They all have operating speeds in the eighty-five to one hundred copy/minute range, and this speed is fixed. Their exposure and development systems will not tolerate variation in speed. Such prior art copiers, by their very nature, are also sensitive to characteristics of the copy material, e.g. the sheet on which the copy is made. In general, those copiers have difficulty making good reproductions on certain coated papers, or on pressure sensitive paper with encapsulated dyes, or on sheets of variable thickness as where a blank label is already adhered to the sheet.